The detection of micro-organisms for medical treatments and security systems has taken on increased importance in recent years. Modern medical systems as well as security systems depend on the detection and identification of microorganisms, including bioagents or toxins in the air, food, water, blood or other specimens.
Conventional detection is usually done in the laboratory. Laboratory testing typically uses skilled personnel in a time consuming process. Portable versions of laboratory PCR (polymerase chain reaction) have been developed, however, these devices are bulky and not cost effective.
Optical systems for detecting and identifying micro-organisms provide numerous advantages over chemical and other analysis techniques. For example, optical systems can reduce or eliminate the need for field workers to use chemical reactions to detect elements. Optical systems are also often nondestructive to the sample being analyzed.
Most optical biosensor designs rely on interactions between light and a biological sample to provide information on sample characteristics. However, the interaction between light and biological elements in the sample is typically weak. Thus without amplification of the interaction, a large quantity of analyte may be needed. Obtaining such large sample sizes may not be practical for many applications.
In order to increase the interaction between light and biological elements in the sample, optical waveguides may concentrate the intensity of light on the sample. In one use, microorganisms in the sample reside in liquid immediately adjacent to a waveguide surface. Evanescent waves from the waveguide interact with the molecules of the biological elements. However, the interaction between the evanescent waves and the biological elements is still weaker than desired.
A related patent application entitled Anti-resonant waveguide sensors, U.S. patent application Ser. No. 10/976,434 by many of the same inventors and assigned to the same assignee describes an improved sensor system and is hereby incorporated by reference. The patent application describes using an anti-resonant waveguide to confine and guide the light within the target-containing medium and therefore increase the interaction region between light and analyte (e.g., biological or chemical agent) being tested. The described system has a number of uses including the detection of binding events.
However, the system has not performed as well as expected. In particular, the light distribution within the anti-resonant waveguide is not as uniform as desired for many applications. Furthermore, in some applications, significant portions of the waveguide need to be devoted to coupling the light and uniformly distributing the light through the waveguide.
Thus an improved system for detection and identification with minimized light coupling region and homogeneous light distribution is needed.